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Abstract:

Various methods and apparatuses for receiving a control channel involve a
communication device monitoring a first control and receiving information
from a network regarding the configuration of a second control channel.
The communication device receives an uplink grant from the network;
transmits a message to the network, in which the message indicates to the
network that the communication device is capable of monitoring the second
control channel. The communication device monitors the second control
channel based on the configuration information receiving via the first
control channel.

Claims:

1. A method in a communication device, the method comprising: monitoring
a first control channel; receiving information from the network regarding
a configuration of a second control channel; during a random access
procedure between the communication device and the network: receiving an
uplink grant from the network, and transmitting a message to the network,
the message including an indication that the communication device is
capable of monitoring a second control channel; monitoring the second
control channel based on the received configuration information.

2. The method in claim 1 wherein receiving an uplink grant from the
network comprises: transmitting a random access preamble to the network;
and receiving the uplink grant from the network in response to the random
access preamble transmission.

3. The method of claim 1, wherein the step of receiving the uplink grant
comprises being granted resources that are usable by the communication
device to transmit messages to the network, and wherein the step of
transmitting message to the network comprises transmitting the message
using the granted resources.

4. The method of claim 3, wherein the granted resources include one or
more resource blocks.

5. The method of claim 1, wherein the communication device is in a first
mode for receiving downlink data, the method further comprising:
receiving, via the first control channel, an identification of a second
mode for receiving downlink data; and receiving downlink data using the
second mode.

6. The method of claim 1, further comprising receiving downlink control
information via the second control channel, and using the downlink
control information to decode data received on a data channel from the
network.

7. The method of claim 1, wherein the step of monitoring the second
control channel comprises attempting to decode downlink control
information on a set of time-frequency resources received on a sub-frame
from the network and, if the attempt is successful, reading the control
information contained in the decoded time-frequency resource.

8. A method in a communication device, the method comprising: receiving a
transmission from a network; determining whether to use a first default
transmission mode or a second default transmission mode based on the
received transmission, wherein the first default transmission mode is
associated with a first type of reference signal and the second default
transmission mode is associated with a second type of reference signal;
receiving data according to the determined first or second default
transmission mode using the associated first or second type of reference
signal.

9. The method according to claim 8 further comprising: determining, based
on the received transmission, whether to operate according to a first
carrier type or a second carrier type; and receiving data according to
the first default transmission mode if operating according to the first
carrier type and according to the second default transmission mode if
operating according to the second carrier type.

10. The method of claim 8, wherein the received transmission is a
broadcast transmission.

11. The method of claim 8, wherein the received transmission is one or
more of a synchronisation signal, a broadcast channel, a Master
Information Block, and a System Information Block.

12. The method of claim 8, wherein the first type of reference signal is
a common reference signal and the second type of reference signal is a
communication device specific reference signal.

13. A method for a communication device, the method comprising:
requesting access to the network via a random access channel; receiving,
in response to the request, an identifier to be used to identify the
communication device to the network; determining whether the identifier
falls into a recognized range; if, based on the determining step, the
identifier falls within the recognized range, responding to the receipt
of the identifier with a message, the message including an indication
that the communication device is capable of monitoring a control channel.

14. The method of claim 13, wherein the control channel is an enhanced
control channel, wherein the responding step comprises responding to the
receipt of the identifier with a message including an indication that the
communication device is capable of monitoring the enhanced control
channel, the method further comprising: if, based on the determining
step, the identifier does not fall within the recognized range,
monitoring transmissions from the network using a legacy control channel;
and if, based on the determining step, the identifier falls within the
recognized range, monitoring transmissions from the network using the
enhanced control channel.

15. A method for a communication device to handover from a first cell to
a second cell, the method comprising: receiving a handover message
indicating that the communication device is to handover from the first
cell to the second cell, the first and second cells operating on the same
carrier frequency, wherein the handover message includes information
regarding one or more of: information regarding time-frequency resources
of a control channel of the second cell, wherein the frequency span of
the time-frequency resources is smaller than the transmission bandwidth
configuration of the second cell, an identification of a set of antenna
ports to be used to communicate via a control channel of the second cell,
and information regarding the energy per resource element of a control
channel of the second cell; performing a handover from the first cell to
the second cell; and receiving, via the said control channel, indication
of resources for at least one of downlink and uplink transmissions.

16. The method of claim 15, wherein information regarding time-frequency
resources of the control channel of the second cell comprises information
regarding a set of resource blocks corresponding to the control channel
of the second cell and the frequency span of the set of resource blocks
is smaller than the transmission bandwidth configuration of the second
cell.

17. The method of claim 15, further comprising, monitoring the control
channel of the second cell using the information included in the handover
message.

18. A method for a communication device to transfer from a first cell to
a second cell, the method comprising: monitoring a first type of control
channel of the first cell; monitoring a second type of control channel of
the first cell; receiving a handover message; in response to receiving
the handover message, monitoring the first type of control channel of the
second cell, wherein the handover message includes an indication of
whether the communication device should monitor the second type of
control channel of the second cell; and monitoring the second type of
control channel of the second cell based on the indication.

19. A method for a communication device to monitor control channels in a
wireless network, the method comprising: during a first time interval,
monitoring a first and a second control channel; receiving a scheduling
message during the first time interval on either the first or the second
control channel; if the scheduling message is received via the first
control channel, monitoring the first control channel and not the second
control channel for a second time interval, if the scheduling message is
received via the second control channel, monitoring the second control
channel and not the first control channel for the second time interval;
wherein the first and second time intervals do not overlap.

20. The method according to claim 19, wherein the first time interval is
a recurring time interval, and wherein the start of successive first time
intervals is predefined.

21. The method according to claim 19, wherein the first time interval
occurs at the start of a discontinuous reception (DRX) cycle.

22. The method of claim 19, wherein the first time interval is a first
time interval spanning one or more subframes and the second time interval
is a second time interval spanning one or more subframes.

23. A communication device comprising: a processor; and a transceiver,
wherein the processor and the transceiver cooperate to perform steps
comprising: monitoring a first control channel; receiving information
from the network regarding a configuration of a second control channel;
during a random access procedure between the communication device and the
network: receiving an uplink grant from the network, and transmitting a
message to the network, the message including an indication that the
communication device is capable of monitoring a second control channel;
monitoring the second control channel based on the received configuration
information.

24. A communication device comprising: a processor; and a transceiver,
wherein the processor and the transceiver cooperate to perform steps
comprising: transmitting a random access preamble to the network; and
receiving the uplink grant from the network in response to the random
access preamble transmission.

25. A communication device comprising: a processor; and a transceiver,
wherein the processor and the transceiver cooperate to perform steps
comprising: receiving a transmission from a network; determining whether
to use a first default transmission mode or a second default transmission
mode based on the received transmission, wherein the first transmission
mode is associated with a first type of reference signal and the second
default transmission mode is associated with a second type of reference
signal; receiving data according to the determined first or second
default transmission mode using the associated first or second type of
reference signal.

Description:

TECHNICAL FIELD

[0001] The present disclosure relates generally to wireless communication,
and more particularly to monitoring control channels in such systems.

BACKGROUND

[0002] In wireless communication systems, especially mobile communication
networks, control signaling is often necessary to support downlink data
channels. Control signaling enables a device in a network to successfully
receive, demodulate, and decode the downlink signals it receives. For
example, in Long-Term Evolution (LTE) networks, the Physical Downlink
Control Channel (PDCCH) and (for LTE Release 11 and beyond) the Enhanced
Physical Downlink Control Channel (EPDCCH) are used for control
signaling. The PDCCH and/or EPDCCH provides a device or User Equipment
(UE) with information that allows the device to, for example, process
data that is downloaded/transmitted from the network (via one or more
base stations) over the Physical Data Shared Channel (PDSCH). The UEs in
an LTE network typically do not "know" exactly where the PDCCH/EPDCCH
control channels are located in the downlink frames received from the
network, and must therefore search the frames to locate the appropriate
control channels. Such searching is often challenging.

[0003] It may be the case that some UEs in LTE networks are capable of
receiving an EPDCCH while other are not. Such a mismatch can introduce
complications. Furthermore, some cells of an LTE network may be capable
of using an EPDCCH while others are not. This may introduce more
complications when a UE is handed over from one cell that is
EPDCCH-capable to one that is not (or vice versa).

[0004] The various aspects, features and advantages of the invention will
become more fully apparent in the following description with the
accompanying drawings described below. The drawings may have been
simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 depicts an example of a communication system in which
various embodiments of the invention may be implemented.

[0006]FIG. 2 shows a block diagram depicting certain aspects of a TP in
accordance with an embodiment of the invention.

[0007] FIG. 3 shows a block diagram depicting aspects of a device that
that may function as a UE in an embodiment of the invention.

[0008] FIG. 4 depicts a sub-frame according to an embodiment of the
invention.

[0009] FIG. 5 shows an example of how the TP of FIG. 1 creates and
transmits a UE-specific control channel in an embodiment of the
invention.

[0010] FIGS. 6-11 depict various techniques for a UE to receive one or
more of a PDCCH and EPDCCH under various conditions according to various
embodiments of the invention.

[0011] In accordance with the foregoing, methods and apparatuses for
receiving a control channel will now be described.

[0012] According to an embodiment of the invention, a method involves a
communication device monitoring a first control channel (e.g., a first
type of control channel, such as a PDCCH) and receiving information from
a network regarding the configuration of a second control channel (e.g.,
a second type of control channel, such as an EPDCCH). The method further
comprises receiving an uplink grant from the network; transmitting a
message to the network, in which the message indicates to the network
that the communication device is capable of monitoring the second control
channel (e.g., the EPDCCH); and monitoring the second control channel
based on the received configuration information of the second control
channel. In an embodiment of the invention, the communication device
receives the uplink grant and transmits the capability message during a
random access procedure (e.g., during a RACH procedure receiving the
uplink grant as part of a msg2 and transmitting the capability message as
part of a new msg3, respectively).

[0013] In an embodiment of the invention, the communication device
receives a transmission from a network (e.g., receiving one or more of a
synchronisation signal, a broadcast channel, a Master Information Block,
and a System Information Block). Based on the transmission (e.g., based
on the synchronisation signal structure (e.g., synchronization sequence,
position of the synchronization sequence within a subframe and/or
time-frequency resources used, synchronization signal bandwidth, type of
synchronization signal, etc.), information received in the broadcast
channel, the Master Information Block, and/or the System Information
Block identifying whether the network is Release 11 capable or not), the
communication uses either a first or a second default transmission mode
(e.g., the communication device uses the default transmission mode based
on the type of network--tm9 if the network is Release 11 capable; tm1 or
2 if not) to receive data from the network (e.g., the PDSCH).

[0014] According to an embodiment, a communication device transmits a
message to a network via a random access channel (e.g., msg1 via RACH).
In response to the transmission, the communication device receives an
identifier (e.g. TC-RNTI). The communication device determines whether
the identifier falls into a recognized range. If the identifier falls
within the recognized range, responding to the receipt of the identifier
with a message indicating that the communication device is capable of
monitoring a control channel (e.g., if the identifier falls within a
range that the device recognizes as signifying that the network is EPDCCH
capable, the device informs the network that it is also EPDCCH capable).

[0015] In an embodiment of the invention, the communication device
receives a message indicating that the communication device is to cease
communicating with the first cell and begin communicating with the second
cell (e.g., a handover message). The handover message includes one or
more of: time-frequency resources of a control channel of the second cell
(e.g., which PRBs that the device is to monitor for the EPDCCH), which
antenna ports the device is to use to communicate via the control channel
(e.g., which antenna ports does the device use to monitor for the
EPDCCH), and energy per resource element information of the second cell
(e.g., information that the device can use to determine the EPRE of the
REs on which it receives the EPDCCH--e.g., ratio of EPDCCH EPRE to
UE-specific RS EPRE within each OFDM symbol containing UE-specific RS,
ratio of EPDCCH EPRE to cell-specific RS EPRE among for each OFDM symbol
containing an EPDCCH).

[0016] The various embodiments disclosed herein are frequently described
in the context of an LTE cellular system. It is to be understood,
however, that the scope of the invention is not limited to LTE and may be
implemented in other types of wireless networks (IEEE 802.11, 802.16,
etc.).

[0017] The various embodiments disclosed herein are frequently described
in the context of an Long Term Evolution (LTE) cellular system. It is to
be understood, however, that the scope of the invention is not limited to
LTE and may be implemented in other types of wireless networks (IEEE
802.11, 802.16, etc.).

[0018] Prior to proceeding with this disclosure, a couple of preliminary
concepts will now be described in accordance with certain embodiments of
the invention. A list of acronyms is provided at the end of this
disclosure to facilitate reading.

[0019] A "channel" according to an embodiment of the invention refers to
one or more paths over which to transmit information. This includes a
logical channel, a transport channel, and a physical channel. As used
herein, "channel" may refer to a logical channel. When describing
embodiments of the invention in the LTE context herein, "channel" refers
to a transport channel, which is characterized by how data is transferred
over the radio interface, including the channel coding scheme, the
modulation scheme, antenna mapping, etc. However, when used in
conjunction with "physical" in this disclosure, "channel" refers to a
physical channel, which, in the LTE context, corresponds to a set of
physical resources (e.g. time-frequency and/or resources, etc) that carry
information from higher layers. Each physical channel may or may not have
a corresponding transport channel. When used in the context of a Channel
State Information (CSI) or Channel Quality information (CQI) or channel
estimation or multipath fading channel, the term "channel" refers to the
wireless propagation channel between the UE and the TP or between the TP
and the UE.

[0020] An "antenna port" according to an embodiment of the invention may
be a logical port that may correspond to a beam (resulting from
beamforming) or may correspond to a physical antenna at a UE or a TP. An
antenna port may be defined such that a channel over which a symbol on
the antenna port is conveyed can be inferred from the effective channel
over which another symbol on the same antenna port is conveyed. More
generally, an antenna port can correspond to any well-defined description
of a transmission from one or more of antennas. As an example, it could
include a beamformed transmission from a set of antennas with appropriate
antenna weights being applied, where the set of antennas itself could be
unknown to a UE. In some particular implementations "antenna port" can
also refer to a physical antenna port at the TP. In certain cases, the
beamforming or precoding applied at the TP may be transparent to the UE.
In other words, the UE need not know what precoding weights are used by
the TP for a particular transmission on the downlink. Typically, a
transmission associated with an antenna port may include transmission of
pilots (or reference signals associated with the antenna port) so that
the receiving device can use the pilots to perform channel estimation and
equalization and subsequent received signal processing e.g. to recover
the transmitted information.

[0021] A "layer" in an embodiment of the invention describes the
relationship among the various protocols and communication technologies
used in, for example, LTE as well as the relationship between those
protocols and the physical signaling. While there are many ways to
conceptualize these relationships, a common method, which will be used
herein, is to refer to three layers: Layer 1, also known as the physical
layer; Layer 2, also known as the Media Access Control (MAC) layer; and
Layer 3, also known as the Radio Resource Control (RRC) layer. Layers 2
and 3 are often referred to as the "higher layers." Layer 1 refers to
those technologies that enable the physical transmission of radio
channels, and the raw bits or symbols contained therein. Layer 2, which
is generally considered to be split into two sublayers: the MAC layer and
the Packet Data Convergence Protocol (PDCP) layer. In general, Layer 2
refers to those technologies that enable functions such as mapping
between transparent and logical channels, error correction through Hybrid
Automatic Repeat Request (HARQ) priority handling and dynamic scheduling,
and logical channel prioritization. Layer 3 handles the main service
connection protocols, such as the Non-Access Stratum (NAS) protocol and
the RRC protocol. It is to be understood, however, that different
conceptualizations of these various technologies is possible, and that
the layers may be organized differently.

[0022] The previously-mentioned use of the term "layer" is not to be
confused with "spatial layer," which refers to spatial multiplexing and
the ability of, for example, multiple antennas to multiplex different
signals in different geometrical positions and orientations.

[0023] A "Radio Network Temporary Identifier" (RNTI) is an identifier used
for communication between the between the eNB and the UE. In LTE, there
are several types of RNTI, including C-RNTI (Cell RNTI), RA RNTI (Random
Access Response RNTI), SI-RNTI (System Information RNTI), SPS C-RNTI
(Semi persistent scheduling C-RNTI), Temporary C-RNTI, and Paging RNTI
(P-RNTI). Some RNTIs may be UE-specific (i.e. assigned on a UE basis,
e.f. C-RNTI, SPS C-RNTI), while some RNTIs are cell-common (e.g. such as
P-RNTI, SI-RNTI, etc). Some RNTIs are fixed by specification (e.g.
SI-RNTI, etc) and some may be explicitly or implicitly assigned. Each
separate physical channel may have its own RNTI. For instance, the
cell-specific broadcast PDCCH scheduling the system information and the
associated physical data shared channel (PDSCH) use the SI-RNTI.
Similarly, UE-specific PDCCH scheduling UE-specific information and the
associated physical data shared channel (PDSCH) may use the C-RNTI.
Typically the RNTIs are used as part of the scrambling sequence
initializations for the associated physical channels and/or as part of
the downlink control information message (e.g. CRC masking operations).

[0024] An example of a network in which an embodiment of the invention
operates will now be described. FIG. 1 illustrates a communication system
100, which includes a network 102. The network 102 includes, TPs 103, 104
and 105 (which may be implemented as eNBs or Remote Radio Heads (RRHs)),
and user equipment (UE) or communication device 106, 107 and 108. Various
communication devices may exchange data or information through the
network 102. The network 102 may be an evolved universal terrestrial
radio access (E-UTRA) or other type of telecommunication network. For one
embodiment, a TP may be a distributed set of servers in the network 102.
In another embodiment, a TP may correspond to a set of geographically
collocated or proximal physical antenna elements. A UE may be one of
several types of handheld or mobile devices, such as, a mobile phone, a
laptop, or a personal digital assistant (PDA). In one embodiment, the UE
may be a wireless local area network capable device, a wireless wide area
network capable device, or any other wireless device. A TP may have one
or more transmitters and one or more receivers. The number of
transmitters at a TP may be related, for example, to the number of
transmit antennas at the TP. Similarly, a UE may have multiple receive
antennas communicating with one or more of the TPs. Each antenna port may
carry signals to a UE from a TP and from the TP to the UE. Each antenna
port may also receive these signals. In one embodiment, the network 100
is capable of using Coordinated Multipoint (CoMP) techniques.

[0025]FIG. 2 illustrates a possible configuration of a TP (e.g., one or
more of the TPs in FIG. 1). The TP may include a processor/controller
210, a memory 220, a database interface 230, a transceiver 240,
input/output (I/O) device interface 250, and a network interface 260,
connected through bus 270. The TP may implement any operating system,
such as Microsoft Windows®, UNIX, or LINUX, for example. Client and
server software may be written in any programming language, such as C,
C++, Java or Visual Basic, for example. The server software may run on an
application framework, such as, for example, a Java® server or
.NET® framework.

[0026] The processor/processor 210 may be any programmable processor. The
subject of the disclosure may also be implemented on a general-purpose or
a special purpose computer, a programmed microprocessor or
microprocessor, peripheral integrated circuit elements, an
application-specific integrated circuit or other integrated circuits,
hardware/electronic logic circuits, such as a discrete element circuit, a
programmable logic device, such as a programmable logic array, field
programmable gate-array, or the like. In general, any device or devices
capable of implementing the decision support method as described herein
may be used to implement the decision support system functions of this
disclosure.

[0027] The memory 220 may include volatile and nonvolatile data storage,
including one or more electrical, magnetic or optical memories such as a
random access memory (RAM), cache, hard drive, or other memory device.
The memory may have a cache to speed access to specific data. The memory
220 may also be connected to a compact disc-read only memory (CD-ROM),
digital video disc-read only memory (DVD-ROM), DVD read write input, tape
drive, or other removable memory device that allows media content to be
directly uploaded into the system. Data may be stored in the memory 220
or in a separate database. The database interface 230 may be used by the
processor/controller 210 to access the database. The database may contain
any formatting data to connect UE to the network 102 (FIG. 1). The
transceiver 240 may create a data connection with the UE.

[0028] The I/O device interface 250 may be connected to one or more input
devices that may include a keyboard, mouse, pen-operated touch screen or
monitor, voice-recognition device, or any other device that accepts
input. The I/O device interface 250 may also be connected to one or more
output devices, such as a monitor, printer, disk drive, speakers, or any
other device provided to output data. The I/O device interface 250 may
receive a data task or connection criteria from a network administrator.

[0029] The network connection interface 260 may be connected to a
communication device, modem, network interface card, a transceiver, or
any other device capable of transmitting and receiving signals from the
network 106. The network connection interface 260 may be used to connect
a client device to a network. The network connection interface 260 may be
used to connect the teleconference device to the network connecting the
user to other users in the teleconference. The components of the TP may
be connected via an electrical bus 270, for example, or linked
wirelessly.

[0030] Client software and databases may be accessed by the
processor/processor 210 from memory 220, and may include, for example,
database applications, word processing applications, as well as
components that embody the decision support functionality of the present
disclosure. A TP (FIG. 1) may implement any operating system, such as
Microsoft Windows®, LINUX, or UNIX, for example. Client and server
software may be written in any programming language, such as C, C++, Java
or Visual Basic, for example. Although not required, the disclosure is
described, at least in part, in the general context of
computer-executable instructions, such as program modules, being executed
by the electronic device, such as a general purpose computer. Generally,
program modules include routine programs, objects, components, data
structures, etc. that perform particular tasks or implement particular
abstract data types. Other embodiments may be practiced in network
computing environments with many types of computer system configurations,
including personal computers, hand-held devices, multi-processor systems,
microprocessor-based or programmable consumer electronics, network PCs,
minicomputers, mainframe computers, and the like.

[0031] FIG. 3 illustrates in a block diagram one embodiment of a
telecommunication apparatus or electronic device to act as a UE (such as
one or more of the UEs depicted in FIG. 1). The UE may be capable of
accessing the information or data stored in the network 102. For some
embodiments of the disclosure, the UE may also support one or more
applications for performing various communications with the network 102.

[0032] The UE may include a transceiver 302, which is capable of sending
and receiving data over the network 102. The UE may include a processor
304 that executes stored programs. The UE may also include a volatile
memory 306 and a non-volatile memory 308 which are used by the processor
304. The UE may include a user input interface 310 that may comprise
elements such as a keypad, display, touch screen, and the like. The UE
may also include a user output device that may comprise a display screen
and an audio interface 312 that may comprise elements such as a
microphone, earphone, and speaker. The UE also may include a component
interface 314 to which additional elements may be attached, for example,
a universal serial bus (USB) interface. Finally, the UE may include a
power supply 316.

[0033] It is to be noted that various embodiments of the inventive methods
described herein may be carried out on the hardware described with
reference to FIG. 3 or FIG. 4, or in some cases both. It is to be
understood that there may be many other components of a UE, TP, network,
or communication system that are known in the art but not depicted in
this disclosure, but that would be used in conjunction with the
embodiments described in this disclosure.

[0034] Referring back to FIG. 1, one or more of the TPs and one or more
the UEs may include one or more transmitters and one or more receivers.
The number of transmitters may be related, for example, to the number of
transmit antennas at the TP and UE. The TP and the UE may also have
multiple antennas. A multiple antenna configuration on either a TP or a
UE is generally supports MIMO communication.

[0035] Referring again to FIG. 1, the general mode of communication of the
system 100 according to an embodiment of the invention will now be
described. Although the communication will often be referred to as taking
place between the network 102 and a UE 106, it is to be understood that
this is for ease of description, and that the communication takes place
between one or more of the TPs of the network 102 and the UE 106.

[0036] The network 102 and the UE 106 generally communicate via physical
UL channels and physical DL channels. The physical medium used for the
communication is Radio Frequency (RF) signals. The RF signals are
transmitted on a carrier frequency with a predefined channel bandwidth.
The modulation scheme used for communication between the network 102 and
the UE 106 differs depending on whether the signals are being sent in the
UL direction (travelling from the UE 106 to network 102) or the DL
direction (travelling from the network 102 to the UE 106). The modulation
scheme used in the DL direction is a multiple-access version of OFDM
called Orthogonal Frequency-Division Multiple Access (OFDMA). In the UL
direction, Single Carrier Frequency Division Multiple Access (SC-FDMA) is
used.

[0037] According to an embodiment of the invention, orthogonal subcarriers
transmitted in the DL direction are modulated with a digital stream,
which may include data, control information, or other information, so as
to form a set of OFDM symbols. The subcarriers may be contiguous or
discontiguous. DL data modulation may be performed using quadrature phase
shift-keying (QPSK), 16-ary quadrature amplitude modulation (16QAM), or
64QAM, although other modulation schemes may be used. The OFDM symbols
are configured into a DL sub-frame. Each OFDM symbol has a time duration
and is associated with a cyclic prefix (CP). A CP is similar to a guard
period between successive OFDM symbols in a sub-frame, but its primary
function is to render the data transmitted on different subcarriers
orthogonal upon application of a Fast Fourier Transform (FFT) in a
receiver in a multipath fading channel.

[0038] The DL data carried by the OFDM signals is organized into radio
frames. Each radio frame typically includes ten sub-frames. An example of
the structure of a sub-frame is shown in FIG. 4, which depicts a
sub-frame 400 represented as a time-frequency diagram. A vertical scale
of the diagram depicts multiple blocks of frequency, also referred to as
frequency bins or frequency subcarriers. A horizontal scale of the
diagram depicts multiple blocks of time (in units of OFDM symbols) of the
sub-frame 400 that may be allocated. The sub-frame 400 comprises multiple
resource blocks (RBs) such as Resource Block 0 (RB0), Resource Block 1
(RB1), Resource Block 2 (RB2), and Resource Block 3 (RB3). Typically,
each RB comprises 12 OFDM subcarriers over a time slot comprising 7 OFDM
symbols. Typically, the sub-frame duration is 1 ms and is organized into
two time slots of 0.5 ms duration each. Each RB can be divided into
multiple resource elements (REs). Each RE is a single OFDM subcarrier, or
frequency bin, on a single OFDM symbol. It is to be noted that many
frames and sub-frames may be transmitted from the network 104 to the UE
106 and vice-versa, and that various channels may occupy slots in many
sub-frames.

[0039] The sub-frame 400 may also be used to carry other signals and
channels such as synchronization signals such as Primary/Secondary
Synchronization channels (P/S-SCH), broadcast control channels, including
primary broadcast control channel (PBCH), etc. The PBCH includes the MIB.
The MIB includes a portion of a system frame number (SFN), downlink
system bandwidth, Physical Hybrid ARQ Channel (PHICH) configuration (such
as duration and PHICH resource indicator), PDCCH and EPDCCH related
(e.g., indication) configuration information (described in more detail
elsewhere).

[0040] To enable DL communication to occur smoothly, the network 102 uses
control signaling, including DL signaling via DL control channels. One
such DL control channel is the Physical Downlink Common Control Channel
(PDCCH) which is located at the start of each DL sub-frame (up to the
first three OFDM symbols). Another is the Enhanced Physical Downlink
Control Channel (EPDCCH) which is located on one or more RB-pairs
spanning both slots in the sub-frame. Each of these channels carries the
DL scheduling assignment, UL scheduling grants, UL transmit power control
commands, etc. In one embodiment, EPDCCH is used in LTE Release 11, and
is an enhanced version of the PDCCH, which is used in LTE Releases 8, 9,
and 10.

[0041] Each of the PDCCH and EPDCCH carries Downlink Control Information
(DCI). DCI provides the UE with information necessary for proper
reception and decoding of downlink data. DCI may include DL information
such as scheduling assignments, including PDSCH resource indication,
transport format, hybrid ARQ information, and spatial multiplexing
control information. DCI may also include UL scheduling grants and UL
information of the same types as the DL information.

[0042] The network 102 (FIG. 1) transmits the PDCCH to the UE 106 in a set
of RBs that span the entire frequency range of the sub-frame 400. In
contrast, the EPDCCH may be transmitted over only a portion of the
frequency range. In the sub-frame 400 of FIG. 4, for example, the UE 106
receives the EPDCCH in RB0 and RB1, i.e., RB-pairs spanning both slots of
the sub-frame, but only part of its frequency range.

[0043] Another example of a downlink channel that can be carried in the
sub-frame 400 is the physical downlink shared channel (PDSCH). The PDSCH
is used to send user data and control information (such as paging
messages) to all mobile devices operating within its coverage area.

[0044] To decode information carried on the PDCCH in an embodiment of the
invention, the UE carries out channel estimation. To perform channel
estimation, UE uses Reference Signals (RS) or pilot symbols that it
receives in the sub-frame 400. The reference signals are associated with
one or more antenna ports. For example, a UE using LTE Release 8, 9, or
10 uses the reference signals associated with one or more of antenna
ports 0, 1, 2, and 3. The RS structure for antenna ports 0, 1, 2, and 3
is shown in FIG. 4, in which R0, R1, R2, R3 are resource elements
carrying reference signals associated with antenna ports 0, 1, 2, and 3
respectively.

[0045] To decode data carried on the PDSCH in an embodiment of the
invention, the UE 106 may use RS received in the sub-frame 400. For
example, a UE using LTE Release 10 the UE can either use reference
symbols associated with one or more of antenna ports 0, 1, 2, or 3, or
use reference symbols associated with one or more of antenna ports 7, 8,
9, 10, 11, 12, 13, 14. The selection of antenna ports to be used is based
on the transmission mode used for PDSCH reception. The concept of a
"transmission mode" is described in more detail elsewhere. A reference
signal associated with antenna ports 7-14 are typically referred to as a
"UE specific reference signal (UERS)" or "Demodulation reference signal
(DMRS)." A reference signal associated with antenna ports 0, 1, 2, 3 is
typically referred to as "Cell-specific Reference Signal (CRS)." While a
CRS is sent across the entire carrier bandwidth by the TP, the DMRS may
only be present in those RBs for which the UE has a PDSCH assignment.

[0046] Another type of reference signal that may be included in the
sub-frame 400 is a Channel State Information Reference Signal (CSI-RS).
The CSI-RS is used by the UE to determine channel-state information (CSI)
that the UE reports to the network 102. In one embodiment, the CSI
includes a Channel Quality Indicator (CQI). The CQI gives the network 102
information about the link adaptation parameters that the UE can support
at that time, taking into account the transmission mode, the receiver
type of the UE, the number of antennas being used by the UE, and the
interference being experienced by the UE. In one embodiment, the CQI is
defined by a sixteen entry table with Modulation and Coding Schemes
(MCS).

[0047] In an embodiment of the invention, a PDCCH is transmitted on one or
an an aggregation of consecutive Control Channel Elements (CCEs). In a
PDCCH, a CCE has 9 Resource Element Groups (REGs), with each REG
containing 4 Resource Elements (REs), for a total of 36 REs.

[0048] In an embodiment of the invention, an EPDCCH is transmitted on one
or an aggregation of enhanced control channel elements (eCCEs). An eCCE
can correspond to a set of REs in a set of resource blocks on which
EPDCCH is transmitted. The set of REs that correspond to an eCCE may be
further grouped into enhanced resource element groups (eREGs). The size
of an eCCE may not be fixed, and may correspond to different number of
REs in different subframes.

[0049] In an embodiment of the invention, each instance of a PDCCH or
EPDCCH has its own configuration. The configuration of a PDCCH or EPDCCH
is indicated by a PDCCH or EPDCCH configuration message respectively. A
"configuration" in this context is described by a set of "attributes."
Possible attributes of a PDCCH or EPDCCH include: CCE size (or eCCE
size), CCE aggregation level (or eCCE aggregation level), localized
transmission of the CCEs (or eCCEs), distributed transmission of the CCEs
(or eCCEs), its transmission scheme, its SNR gain, the set of RBs in
which it is contained, the antenna ports it uses, the number of antenna
ports it uses, the number of spatial layers it uses, the scrambling
sequence for its (EPDCCH or PDCCH) coded bits, initialization or portion
of the initialization or parameters for computing the initialization of
the scrambling sequence generator for the scrambling sequence for PDCCH
or EPDCCH coded bits, UERS or DMRS sequence or DMRS scrambling sequence,
initialization or portion of the initialization parameters for computing
the initialization (e.g, DMRS scrambling sequence identifier) of the
scrambling sequence generator for DMRS sequence, DMRS signature sequence
(sequence used to modulate the DMRS sequence), its modulation, and the
PDCCH or EPDCCH to reference signal (e.g., DMRS) power boost ratio, which
is determined, for example, from the ratio of the Energy Per Resource
Element (EPRE) of the PDCCH or EPDCCH to that of the reference signal
(e.g., DMRS).

[0050] An example of two EPDCCHs having configurations that differ in one
or more attributes is as follows: EPDCCH configuration #1 has 4 eCCEs,
DMRS port #7, RBs {#5, #20, #35, #45}, 0 dB power boost. EPDCCH
configuration #2 has 8 eCCEs, DMRS port #7, RBs {#5, #20, #35, #45}, 3 dB
power boost. Thus, the two configurations differ in 2 attributes: # of
eCCEs and power boost.

[0051] To receive the PDCCH or the EPDCCH in accordance with an embodiment
of the invention, a UE monitors a set of PDCCH or EPDCCH candidates
(e.g., candidate RBs). In this context, "monitoring" refers to the UE
attempting to decode each of the candidates in the PDCCH or EPDCCH
candidate set according to all applicable DCI formats for that candidate.
The set of EPDCCH or PDCCH candidates to be monitored by UE, that is, the
EPDCCH or PDCCH candidate set, can also be defined in terms of search
spaces. The EPDCCH or PDCCH candidates that UE monitors may include a set
of Common Search Space (CSS) candidates, and a set of UE Specific Search
Space (UESS) candidates. The UESS corresponding to EPDCCH may optionally
be called an enhanced UESS (eUESS). CSS candidates are monitored by all
UEs in a cell, while UESS candidates are specific to individual UEs and
are monitored by the UEs for which they are intended.

[0052] When monitoring the CSS, a UE starts decoding from a CCE or eCCE
with known logical index (e.g. CCEO). This restriction further simplifies
the common search. The UE attempts to decode every possible PDCCH or
EPDCCH candidate set for given PDCCH or EPDCCH format until it
successfully decodes the PDCCH or EPDCCH that is present in the CSS.

[0053] To optimize the searching process in an embodiment of the
invention, CCEs (eCCEs) may be aggregated into groups, or "aggregations,"
which are searched together. The sizes of the aggregations (i.e., how
many CCEs or eCCEs are therein) are classified into "aggregation levels."
For example, an search space Sk.sup.(L) at aggregation level L can
refer to a set of candidates in which each candidate in the search space
has L aggregated CCEs (or eCCEs). A PDCCH may have aggregations of 1, 2,
4, and 8 CCEs, with each CCE including 36 REs. An EPDCCH may also have
aggregations of 1, 2, 4, and 8 CCEs (or eCCEs). However, since the size
of the CCEs (or eCCEs) of an EPDCCH is not fixed, other aggregation
levels (e.g. L=3 or L=12) may be used. Also, since the size of the EPDCCH
CCEs (or eCCEs) can change considerably between different sub-frames and
slots within a sub-frame (for example, based on control region size,
presence of CSI-RS, and sub-frame type), a set of aggregation levels that
the UE 106 assumes for EPDCCH monitoring also may vary between sub-frames
or between slots in a same sub-frame or between different sub-frame types
(for example, a normal sub-frame vs. an MBSFN sub-frame). More generally,
a set of aggregation levels that the UE assumes for EPDCCH monitoring can
vary between over time.

[0054] An example of how the TP 104 (FIG. 1) creates and transmits a
UE-specific EPDCCH or PDCCH and how the UE 106 extracts the EPDCCH or
PDCCH intended for the UE 106 will now be described with reference to
FIGS. 1 and 4, and to FIG. 5. For the sake of simplicity, this example
will be described in the context of EPDCCH, though it is to be understood
that the process may be the same for a PDCCH.

[0055] Preliminarily, the UE 106 performs a random access to the network
102 using a Random Access Channel (RACH) (FIG. 5). In doing so, the UE
106 transmits a RACH preamble sequence, referred to as msg1, to the TP
104. The UE 106 receives a RACH response, referred to here as msg2, from
the TP 106. The msg2 contains an identifier called a Temporary C-RNTI
(TC-RNTI). The UE 106 transmits a msg3 to the network 102, which
identifies the UE 106 to the network 102. Specifically, the UE 106 uses a
pre-existing C-RNTI or another pre-existing identifier to identify
itself. If the UE 106 has been previously identified to the network 102,
then the UE 106 already has a C-RNTI, and uses that C-RNTI to identify
itself. Otherwise, the UE 106 uses another pre-existing identifier such
as S-TMSI (S-Temporary Mobile Subscriber Identity). After transmitting
msg3, the UE 106 uses the TC-RNTI (or C-RNTI) to monitor the PDCCH for
uplink grants and downlink assignments. Once the UE receives a message
indicating successful contention resolution--a msg4--it promotes its
TC-RNTI to a C-RNTI if it does not already have a C-RNTI. The UE then
continues monitoring the UESS using the C-RNTI.

[0056] Once the TP 104 and UE 106 have completed the RACH process, the TP
104 creates an EPDCCH message. To do so, the TP 104 determines the
appropriate EPDCCH format, creates the appropriate DCI and attaches a
CRC. The CRC is then masked with an RNTI. Which RNTI is used depends of
the purpose for with the EPDCCH is to be used. If, for example, the
EPDCCH is for a specific UE, the CRC will be masked with the C-RNTI of
the specific UE. Other RNTIs may be used in other scenarios.

[0057] To obtain the control information from the EPDCCH, the UE 106
carries out blind decoding. In other words, the UE 106 monitors a set of
EPDCCH candidates (a set of consecutive CCEs (or eCCEs) on which EPDCCH
could be mapped) in every sub-frame. The UE 106 de-masks each EPDCCH
candidate's CRC using the C-RNTI. If no CRC error is detected, the UE 106
considers it as a successful decoding attempt and reads the control
information within the successful EPDCCH candidate.

[0058] It is to be noted that there are possible variations on the above
procedure. For example, if the EPDCCH contains paging information, the
CRC may be masked with a paging indication identifier, i.e., P-RNTI. If
the EPDCCH contains system information, a system information identifier,
i.e., a SI-RNTI, may be used to mask the CRC.

[0059] In accordance with an embodiment of the invention, in order to
receive the PDSCH, a UE may be configured with a transmission mode from
among multiple known transmission modes. During initial access to the
network, that is, before receiving transmission mode configuration
signaling from the network 102, the UE 106 can receive the PDSCH by
assuming a default value for transmission mode. In LTE Releases 8, 9, and
10, the default values for transmission mode are tm1 for a one CRS
antenna port system and tm2 for a two CRS antenna port system. In LTE
Release 11, the default value for transmission mode is tm9. The network
102 can subsequently configure the UE with other non-default values for
transmission modes to receive PDSCH. The aspect of UE receiving PDSCH
using a default value for transmission mode is also referred to as
receiving PDSCH using a "default transmission mode".

[0060] According to various embodiments, each transmission mode has
certain attributes. For example, if the UE is configured with
transmission mode 2, the UE can receive the PDSCH using CRS and a
transmit diversity transmission scheme. If the UE is configured with
transmission modes 3, 4, 5, or 6, the UE can receive the PDSCH using CRS
and Multiple Input Multiple Output (MIMO) based transmission schemes such
as open loop spatial multiplexing, closed loop spatial multiplexing and
Multi-User MIMO (MU-MIMO). If the UE is configured with transmission
modes 7 or 8, the UE can receive the PDSCH using UE-specific RSs. If the
UE is configured with transmission mode 9, the UE can receive the PDSCH
using DMRS, and spatial multiplexing of up to eight spatial layers is
possible. Transmission mode 9 is suitable for PDSCH reception using
features such as CoMP and MIMO techniques such as MU-MIMO. Configuring
the UE in transmission mode 9 also allows for beamformed
frequency-selective transmission of the PDSCH to the UE.

[0061] In an embodiment of the invention, in order to provide the required
data bandwidth, several carriers may be used together in a process called
carrier aggregation (CA). Using this processes several carriers are
aggregated on the physical layer to provide the required bandwidth. To an
a UE that is not capable of using CA terminal, each component carrier
appears as a separate carrier, while a UE that is CA-capable can exploit
the total aggregated bandwidth of the multiple carriers as if they were a
single carrier.

[0062] When carrier aggregation is employed, at least one of the TPs acts
as the "primary cell" or Pcell, and the other TPs act as secondary cells
or Scells. The Pcell is often referred to as the "anchor cell," and its
carrier is often referred to as the "anchor carrier". The Pcell is the
cell that operates on the primary frequency, to which the UE (1) performs
an initial connection establishment procedure, (2) initiates the
connection re-establishment procedure, or (3) is indicated as the primary
cell in a handover procedure. The Scell, on the other hand, is a cell
that operates on a secondary frequency, which may be configured once an
RRC connection is established.

[0063] In an embodiment of the invention a type of Scell is New Carrier
Type (NCT). An NCT does not transmit one or more of a CRS, a PSS, an SSS,
or paging signals.

[0064] According to an embodiment of the invention, one or more of the UEs
may employ the technique of Discontinuous Reception (DRX). This technique
allows a terminal to put its frequency modem into a sleep state for long
periods, activating it only in well defined, suitable, instants. This
keeps the terminal from having to continuously monitor control channels.

EPDCCH UESS Monitoring

[0065] Referring to FIG. 6, one scheme for EPDCCH based UESS monitoring
will now be described. In this embodiment, the network configures the UE
to monitor for the EPDCCH by transmitting EPDCCH configuration
information to the UE via the PDCCH. For example, the UE may monitor the
UESS for the PDCCH. The UE eventually identifies and successfully decodes
the PDCCH meant for it. Over the PDCCH, the network sends, for example,
DL assignments scrambled via TC-RNTI to the UE. The network may also use
the PDCCH to send higher layer (MAC/RRC) messages to the UE, such as
messages requesting UE capability, messages that indicate the RBs/RB
pairs on which the UE is to monitor for the UESS-based EPDCCH (i.e.,
EPDCCH based UESS candidates or eUESS candidates), and messages that
configure the UE to monitor for the UESS-based EPDCCH.

[0066] In an embodiment of the invention, the network may also change the
transmission mode of the UE from one transmission mode to another using
the same RRC message that the network uses to configure the UE to monitor
for the UESS-based EPDCCH. For example, in LTE, EPDCCH and PDSCH both use
a DMRS-based transmission mode. In some implementations of LTE,
transmission mode 9 allows both PDSCH and EPDCCH to be received at the
same time using different DMRS antenna ports. The network could send a
message to the UE to configure it to use transmission mode 9 and a
message that configures the UE to monitor for the EPDCCH in a single RRC
message

[0067] In a more specific example, if the network supports both Release
8/9/10 UEs and Release 11 UEs, the network can reuse the same initial
setup signaling for both types of UEs. After the network receives UE
capability/category information from the UEs, the network can
individually configure Release 11 UEs for EPDDCH UESS monitoring.

[0068] In some embodiments, the network 102 does not know whether a UE 106
is EPDCCH-capable (e.g., whether the UE is a Release 11 UE). In one
implementation, the UE 106 first determines a `default` EPDCCH
configuration. The UE then informs the network that it is EPDCCH-capable
during a RACH procedure as follows: The UE transmits a RACH preamble
sequence (msg1) to the network. In response, it receives a RACH response
(msg2) and the RACH response contains TC-RNTI. The UE uses the TC-RNTI
(or C-RNTI, as explained elsewhere) to identify itself in its subsequent
UL transmissions (and to scramble its UL transmissions). The UE transmits
what will be referred to as `new msg3` to the network. The new msg3
includes a unique identifier that is associated with the UE (e.g. a
TMSI). The new msg3 also includes bits or information that indicate to
the network that the UE is capable of supporting EPDCCH reception.

[0069] Some possible bits that the UE may use to inform the network that
the UE is EPDCCH-capable are as follows: (1) The UE can use bit(s) in a
"criticalExtensionsFuture" field in a "RRCConnectionRequest" message of
the new msg3 to indicate to the network that it is capable of supporting
EPDCCH reception. (2) The UE can use a spare bit in a
"RRCConnectionRequest-r8-IEs" information element in a
"RRCConnectionRequest" message of the new msg3 to indicate to the network
that it is capable of supporting EPDCCH reception. (3) The UE can use
spare bit(s) in a "EstablishmentCause" information element in a
"RRCConnectionRequest" message of the new msg3 to indicate to the network
that it is capable of supporting EPDCCH reception.

[0070] It should be noted that the embodiments described previously may
vary with respect to the order in which functions are carried out and
which actions are "cause" and which are "effect." For example, when a UE
transmits a preamble sequence as part of a RACH procedure, the TP
receiving the preamble may be an Scell, while the UL grant may be
transmitted to the UE by the Pcell. Thus, the "response" to the preamble
sequency may be made by a TP other than the "recipient" of the preamble
sequence.

[0071] After transmitting the new msg3, the UE starts monitoring EPDCCH
using the default EPDCCH configuration. By virtue of the information in
the new msg3, the network now knows that the UE is EPDCCH-capable and
therefore can begin to send UE-specific EPDCCH control signals using the
default EPDCCH configuration.

[0072] The default EPDCCH configuration can include information
identifying a set of PRB-pairs (Physical resource block pairs) on which
the UE monitors EPDCCH. The set of PRB-pairs is usually smaller than the
transmission bandwidth configuration of the carrier on which EPDCCH is
monitored. For example, if the transmission bandwidth configuration of a
carrier is 100 RBs (this corresponds to 20 MHz carrier or channel
bandwidth, each RB can logically correspond to a PRB-pair), the default
EPDCCH configuration can include information identifying a set of 4
RB-pairs within the 100 RBs. The default EPDCCH configuration can also
include information identifying a set of antenna ports based on which the
UE can receive EPDCCH. The default EPDCCH configuration can also include
information using which the UE can determine the EPRE (energy per
resource element) of the REs (resource elements) on which it receives
EPDCCH.

[0073] The default EPDCCH configuration is determined by the UE based on a
signal from the network. The signal from the network can include one or
multiple bits of information transmitted by a TP in the network. The bits
may be transmitted as part of the MIB or one of the SIBs. SIBs are
received by the UE on PDSCH RBs assigned via CSS PDCCHs whose CRC is
scrambled with SI-RNTI. In one implementation, the signal from the
network is a message (included in MIB or SIBs) that explicitly indicates
the default EPDCCH configuration to the UE. In another implementation,
the UE may implicitly determine the default EPDCCH configuration using a
signal from the network. For example the UE may determine the default
EPDCCH configuration using a cell identifier (or a transmission point ID)
of an eNB (or a transmission point) in the network. For example, the UE
may use network signals such as PSS (Primary synchronization signal), SSS
(secondary synchronization signal), CRS (cell-specific reference signal)
or CSI-RS (CSI reference signal or Channel state information reference
signal) to determine an identifier associated with an eNB or a
transmission point of the network. For example, the identifier can be a
PCID (Physical cell identifier) or a TP-ID (transmission point
identifier). The UE can then use the identifier to implicitly determine
the default EPDCCH configuration to receive EPDCCH.

[0074] The default EPDCCH configuration can correspond to a set of PRB
pairs on which the UE monitors EPDCCH candidates that are transmitted
using a distributed mapping format. When EPDCCH is transmitted using
distributed mapping, each CCE (or eCCE) of the monitored EPDCCH candidate
is mapped to more than on PRB-pair.

[0075] After the UE starts monitoring UESS-based EPDCCH candidates using
the default EPDCCH configuration, it may receive higher layer signaling
configuring it to monitor EPDCCH candidates using an additional EPDCCH
configuration. After receiving such signaling, the UE may monitor EPDCCH
candidates based on both the default EPDCCH configuration and the
additional EPDCCH configuration. The additional EPDCCH configuration can
be signaled to the UE using RRC signaling in a dedicated RRC message
(e.g. a "RRCConnectionReconfiguration" message that includes a
"radioResourceConfigDedicated" field). The additional EPDCCH
configuration can include information identifying additional sets of
PRB-pairs and antenna ports to monitor EPDCCH. The sets of PRB-pairs
identified in the default EPDCCH configuration and the additional EPDCCH
configuration can overlap.

[0076] For receiving PDSCH, an EPDCCH-capable UE can use the same
CRS-based transmission mode as non-EPDCCH capable UEs. For example, a
Release 11 UE can use the same CRS-based default transmission modes that
Release 8, 9, and 10 UEs use for receiving SIBs and RACH responses (i.e.,
tm1 for the 1 CRS antenna port case and tm2 for the 2 CRS antenna port
case). However, after transmitting the new msg3 the UE can receive PDSCH
using a new default transmission mode that allows it to receive PDSCH
using DMRS (e.g. tm9). This is because when the network receives the new
msg3, it will know the UE is EPDCCH capable (e.g., is a Release 11 UE),
and can begin sending the PDSCH to the UE using tm9.

[0077] FIG. 7 shows an example implementation of these features. As shown,
the UE monitors CSS using PDCCH. The UE also receives a default EPDCCH
configuration from the network using one of the above-described methods.
After transmitting the new msg3 the UE starts monitoring EPDCCH UESS
using the default EPDCCH configuration. Similarly, after receiving the
msg3, the network sends UESS-based EPDCCH information to the UE. If the
UE is not configured with a C-RNTI, the UE initially monitors EPDCCH UESS
using a Temporary C-RNTI (TC-RNTI) and after contention resolution is
successful, it promotes the TC-RNTI to a C-RNTI and monitors EPDCCH UESS
using C-RNTI. Also, the UE can receive additional EPDCCH configuration
from higher layers (e.g. RRC) to monitor additional EPDCCH UESS
candidates using C-RNTI.

[0078] According to another embodiment, the eNB may not always be able to
schedule using EPDCCH in response to the new msg3. For example, (a) the
eNB may want to use a different EPDCCH configuration than the default
configuration, (b) the eNB may not want to use EPDCCH for this particular
UE (e.g., it may be a delay tolerant "Machine type" UE (typically engaged
in Machine Type Communications) and the eNB prefers to use EPDCCH
capacity for conventional UEs), or (c) the eNB may not have enough EPDCCH
capacity. In such cases, the eNB would need to schedule the UE using
PDCCH. In order to enable this, the UE can be configured to monitor for
both PDCCH and EPDCCH after transmitting msg3. If the first transmission
from the eNB to the UE is via EPDCCH, the UE switches to an EPDCCH-only
mode; if the first transmission from the eNB to the UE is via PDCCH, the
UE switches to a PDCCH only mode. During the period when the UE is
monitoring both EPDCCH and PDCCH candidates, the UE's blind decodes are
split between PDCCH and EPDCCH (i.e., not all aggregation levels can be
used for either PDCCH or EPDCCH). Once the UE switches to EPDCCH-only
mode or PDCCH-only mode, all the blind decodes can be used towards EPDCCH
or PDCCH respectively.

[0079] In some implementations, the UE receives a signal from the network,
based on the received signal, can determine which transmission mode to
use to receive the PDSCH. If the nature and content of the signal
indicate that the network is not an EPDCCH-capable network, then the UE
may choose to receive PDSCH using a first default transmission mode
(i.e., receive PDSCH using a first default value for transmission mode).
If the signal indicates that the network is not an EPDCCH-capable
network, then the UE may choose to receive the PDSCH in a second default
transmission mode (i.e., receive PDSCH using a second default value for
transmission mode). For example, if the signal indicates that the network
is an LTE Release 8/9/10 network, then the UE may adopt a Release 8/9/10
default transmission mode--tm1 or tm 2--in which the PDSCH is received
based on CRS. If, on the other hand, the signal indicates that the
network is an LTE Release 11 (or other future release) network, then the
UE may adopt a Release 11 default transmission mode--tm9--in which the
PDSCH is received based on DMRS. The UE can receive PDSCH using the
second default transmission mode until it receives a higher layer message
configuring the UE to receive PDSCH using a different transmission mode
(i.e., a configured transmission mode rather than a default transmission
mode).

[0080] The signal from the network can include one or multiple bits of
information transmitted by an eNB in the network. The bits may be
transmitted as part of MIB or one of the SIBs. In one implementation, the
signal from the network is a message (included in MIB or SIBs) that
explicitly indicates parameters relevant for receiving PDSCH using the
second default transmission mode. For example, the parameters can include
DMRS antenna ports based on which PDSCH is received in the second default
transmission mode, and/or, information indicating zero power CSI-RS RE
locations based on which the UE determines the REs used for receiving
PDSCH in the second default transmission mode, and/or, information
indicating non-zero power CSI-RS RE locations based on which the UE
determines the REs used for receiving PDSCH in the second default
transmission mode. Alternately, the signal from the network may be one or
more of PSS (Primary synchronization signal), SSS (secondary
synchronization signal), CRS (cell-specific reference signal) or CSI-RS
(CSI reference signal or Channel state information reference signal). In
one implementation, if UE determines from the Synchronization Signals
that it is operating on a first carrier type (e.g. a type that supports
only EPDCCH), it will use tm9 as the default value of transmission mode
for receiving PDSCH. Otherwise, if it determines from the Synchronization
Signals that it is operating on a legacy carrier type (e.g. a type that
supports only PDCCH or both PDCCH and EPDCCH), it will use tm1/tm2 as the
default value for tm.

[0081] In an embodiment, illustrated in FIG. 8, if control and balancing
of load between PDCCH and EPDCCH is necessary, then the temporary C-RNTI
can be used to control when UEs will indicate that they are EPDCCH
capable. In this implementation (1) The network reserves a C-RNTI range
to be used for EPDCCH capable UEs. This range can be advertised in system
information or can be fixed in a commonly understood specification. The
network subsequently determines a need to schedule incoming EPDCCH
capable UEs using EPDCCH. (2) The UE transmits a RACH preamble as part of
a connection establishment procedure. (3) If there is available EPDCCH
capacity, the TP responds with an RACH response including an UL grant and
a TC-RNTI from the C-RNTI range for EPDCCH capable UEs. (3)(a) A Rel 11
EPDCCH capable UE recognizes the TC-RNTI as belonging to range. The UE
transmits a new msg3. (3)(b) A UE not capable of EPDCCH (including legacy
UEs) transmits a legacy msg 3. (4) If the TP receives a new msg3, it
schedules a msg4 and subsequent transmissions to the UE using EPDCCH.
Otherwise the TP uses PDCCH. If contention resolution succeeds, the UE
uses the TC-RNTI of step 3 as the C-RNTI. It should be noted that the
reserved C-RNTI range is not exclusive to EPDCCH capable UEs. That is,
all EPDCCH capable UEs receive TC-RNTIs from the reserved C-RNTI range,
but non-EPDCCH capable UEs may also receive TC-RNTIs from this range.

[0082] In some embodiments, the resource allocation (e.g. location of the
PRBs within the transmission bandwidth configuration of a carrier) in the
scheduling grant for the RACH response (msg2) can be used to implicitly
indicate whether EPDCCH or PDCCH or a combination of EPDCCH and PDCCH (on
the same or different subframes) is to be used or supported for a Rel-11
or later UE. A UE not capable of EPDCCH (including legacy UEs) would
monitor only PDCCH. Alternatively, the resource allocation (e.g. location
of the PRBs) for the msg3 uplink transmission can indicate whether EPDCCH
or PDCCH or a combination of EPDCCH and PDCCH (on the same or different
subframes) is to be used for a Rel-11 or later UE.

[0083] In one embodiment of the invention, the CSS is monitored for the
PDCCH only in sub-frames not configured as MBSFN sub-frames (e.g.,
sub-frames 0, 4, 5, or 9). In such a scenario, the number of EPDCCH UESS
blind decoding candidates in MBSFN sub-frames can be increased. For
example, in subframes configured as MBSFN subframes the UE may perform
blind decoding for 44 EPDCCH candidates (e.g 8 candidates at aggregation
level 1, 8 candidates at aggregation level 2, 3 candidates at aggregation
level 4 and 3 candidates at aggregation level 8 for two different DCI
format sizes), in subframes not configured as MBSFN subframes, the UE may
perform blind decoding for 32 EPDCCH candidates (e.g 6 candidates at
aggregation level 1, 6 candidates at aggregation level 2, 2 candidates at
aggregation level 4 and 2 candidates at aggregation level 8 for two
different DCI format sizes).

EPDCCH Monitoring--Handover Scenarios

[0084] When a UE gets handed over from one serving cell to a different
serving cell (e.g. based on the handover message(s)), the EPDCCH
configuration may be included in a handover message.

[0085] FIG. 9 shows an example. The UE monitors CSS using PDCCH. To
determine the mapping of PDCCH REs the UE uses a first cell ID. The UE
also monitors UESS using EPDCCH. The UE may determine the mapping of
EPDCCH REs using a previously determined EPDCCH configuration (e.g.,
based on a default EPDCCH configuration and/or additional EPDCCH
configuration signaled by the network). The UE receives a handover
message ordering the UE to handover from the first cell to a second cell.
In some implementations, a handover message is a
"RRCConnectionReconfiguration" message including a "mobilityControlInfo"
information element. After receiving the handover message, the UE
continues to monitor a CSS using PDCCH. However, to determine the mapping
of PDCCH REs, the UE uses a second cell ID (cell ID of the second cell).
After receiving the handover message, the UE also continues to monitor a
UESS using EPDCCH. However, to determine the mapping of EPDCCH REs, the
UE uses information in the handover message.

[0086] In one implementation (as shown in FIG. 9), the information in the
handover message is a new EPDCCH configuration that is received in the
handover message. The new EPDCCH configuration can include information
identifying a set of PRB-pairs (Physical resource block pairs) of the
second cell that the UE monitors for the EPDCCH. The set of PRB-pairs is
usually smaller than the transmission bandwidth configuration of the
carrier associated with the second cell. For example, if the transmission
bandwidth configuration of the carrier is 100 RBs (this corresponds to 20
MHz carrier bandwidth, each RB can logically correspond to a PRB-pair),
the new EPDCCH configuration can include information identifying a set of
4 RB-pairs within the 100 RBs. The new EPDCCH configuration can also
include information identifying a set of antenna ports based on which the
UE can receive EPDCCH in the second cell. The new EPDCCH configuration
can also include information using which the UE can determine the EPRE
(energy per resource element) of the REs (resource elements) on which it
receives EPDCCH of the second cell.

[0087] In another implementation, the handover message can include an
identifier associated with the second cell (e.g. PCID of second cell).
The UE can implicitly determine a set of PRB-pairs of the second cell
(for EPDCCH monitoring) based on the identifier. The UE may also
implicitly determine a set of antenna ports of the second cell (for
EPDCCH monitoring) based on the identifier associated with the second
cell. Alternately, the UE may use the same antenna ports that were used
for EPDCCH monitoring in the first cell.

[0088] In some implementations, if a new EPDCCH configuration is not
received in the handover message, the UE continues using its current
EPDCCH configuration for monitoring UESS of the second cell.

[0089] Another approach to enable EPDCCH monitoring after handover is to
allow the UE to monitor EPDCCH based on a new default EPDCCH
configuration after handover. FIG. 10 shows an example. The UE monitors
EPDCCH using a default EPDCCH configuration of a first cell (default
config.) and an additional EPDCCH configuration (additional config.). The
UE may determine the default EPDCCH configuration of the first cell
implicitly based on an identifier associated with the first cell. For
example, the UE may use signals such as PSS (Primary synchronization
signal), SSS (secondary synchronization signal), CRS (cell-specific
reference signal) or CSI-RS (CSI reference signal or Channel state
information reference signal) to determine an identifier associated with
the first cell. Alternately, the UE may determine the default EPDCCH
configuration of the first cell based on a field or information element
received in a MIB (Master Information Block) or one of the SIBs (System
Information Blocks, e.g. SIB1 or SIB2). The UE may receive the additional
EPDCCH configuration in a dedicated RRC message (e.g. a
"RRCConnectionReconfiguration" message that includes a
"radioResourceConfigDedicated" field). The UE receives a handover message
indicating the UE to handover from the first cell to a second cell. After
receiving the handover message, the UE discontinues EPDCCH monitoring
using the additional EPDCCH configuration and switches to EPDCCH
monitoring using a new default EPDCCH configuration associated with the
second cell. The UE can determine the new default EPDCCH configuration of
the second cell implicitly based on an identifier associated with the
second cell. Alternately, the UE may determine the default EPDCCH
configuration of the second cell based on a field or information element
received in a MIB (Master Information Block) or one of the SIBs (System
Information Blocks, e.g. SIB1 or SIB2) after receiving the handover
message.

[0090] In some implementations, the UE receives a handover message
indicating the UE to handover from the first cell to a second cell and
the UE monitors EPDCCH using a new default EPDCCH configuration if an
EPDCCH configuration is not received in the handover message.

[0091] In some cases when the UE gets handed over from a first cell to a
second cell, the UE may have to discontinue EPDCCH monitoring and start
monitoring PDCCH. This can happen for example when the second cell does
not support EPDCCH or has not allocated any resources for EPDCCH. To
enable the UE to quickly start monitoring a control channel after
handover (either PDCCH or EPDCCH depending on the use case) it is
beneficial to include an indication in the handover message based on or
which the UE uses to decide which control channel to monitor.

[0092]FIG. 11 shows an example. The UE monitors CSS using PDCCH. To
determine the mapping of PDCCH REs the UE uses a first cell ID. The UE
also monitors UESS using EPDCCH. The UE may determine the mapping of
EPDCCH REs using previously determined EPDCCH configuration (e.g., based
on a default EPDCCH configuration and/or additional EPDCCH
configuration). The UE receives a handover message indicating the UE to
handover from the first cell to a second cell. After receiving the
handover message, the UE continues to monitor a CSS using PDCCH. However,
to determine the mapping of PDCCH REs, the UE uses a second cell ID (cell
ID of the second cell). Within the handover message, the UE receives an
indication based on which it determines whether to monitor UESS using
PDCCH or EPDCCH. The indication can be explicit (e.g. an information
element or field in the handover message). Alternately, the indication
can be implicit. For example, the UE monitors UESS using EPDCCH in the
second cell if a specific field (e.g. EPDCCH configuration field) is
present in the handover message, and it monitors UESS using PDCCH if the
specific field is absent in the handover message. Another example of
implicit indication can be--if a "transmissionMode" field in the handover
message configures the UE to use a first transmission mode (e.g., tm1 or
tm2 or . . . tm8), the UE monitors UESS using PDCCH in the second cell,
and if the field in the handover message configures the UE to use a
second transmission mode (e.g., tm9) the UE monitors UESS using EPDCCH in
the second cell.

[0093] In another approach, the UE receives a handover message indicating
the UE to handover from the first cell to a second cell. After receiving
a handover message, the UE transmits a handover complete message. The
handover complete message can indicate whether the UE is EPDCCH capable.
The UE also transmits a RACH after receiving the handover message (using
the RACH configuration included in the handover message). After
transmitting a RACH, the UE receives a RACH response. The UE determines
whether to monitor EPDCCH based on an indication in the RACH response
(e.g. based on the TC-RNTI field).

[0094] In some implementations, in order for a new UE (e.g. Rel11 or Rel12
UE) to operate in both a legacy network (i.e., a network that does not
support EPDCCH) and a "new network" the UE can have two modes. (1) In a
first mode (legacy mode), the UE monitors its CSS/UESS using PDCCH (2) In
a second mode (new mode or non-legacy) the UE monitors its CSS/UESS using
EPDCCH

[0095] The UE can determine whether to operate in legacy mode or new mode
based on spare bits in MIB (received on a CRS based Physical Broadcast
Channel--PBCH), or by looking for a new MIB (received on a DMRS based
Enhanced Physical Broadcast Channel--EPBCH).

[0096] In one implementation the UE receives spare bits in a MIB and the
spare MIB bits tell the UE to receive a new MIB. The UE determines a
default EPDCCH configuration using information in either spare bits in
the MIB or the new MIB.

[0097] In one example, one of the spare MIB bits is set to `0` (or first
value) in the legacy network and the bit is set to `1` (or second value)
in the new network. If a new UE reads the `0` value (or first value) for
the specified MIB bit, it monitors PDCCH based CSS/UESS. If the UE reads
the `1` value (or second value) for the specified MIB bit, it monitors
EPDCCH based CSS/UESS.

[0098] In a network that supports both new UEs and legacy UEs, the network
has to distinguish between new UEs and legacy UEs. The network do this by
configuring the new UEs to use a reserved set of time/frequency/code
domain RACH resources that may be different from (or a subset of) the
RACH resources used by the legacy UEs. This configuration information can
be signalled to the UEs using one or multiple bits of information
transmitted by an eNB in the network. For instance, the bits may be
transmitted as part of MIB (sent on PBCH) or one of the SIBs (sent on
PDSCH RBs assigned via CSS PDCCHs whose CRC is scrambled with SI-RNTI).
If MIB signaling is used, in one instance, one of the reserved MIB bits
is set to `0` (or first value) in the legacy network and the bit is set
to `1` (or second value) in the new network. If a new UE reads the `0`
value (or first value) for the specified MIB bit, it uses the "default
RACH resources" for transmitting a RACH. "Default RACH resources" may be
same as the resources that Rel8/9/10 UEs use for RACH transmission and
these are typically communicated in a SIB2. If the new UE reads the `1`
value (or second value) for the specified MIB bit, it uses "new RACH
resources" for transmitting a RACH. Information about the "new RACH
resources" can be communicated to the UE using an extension to SIB2.
Alternately, the UE may determine the new RACH resources using
information about the old RACH resources and a predefined mapping rule.
The new RACH resources may be a set of RBs that are different from the
RBs used by Rel8/9/10 UEs for RACH transmission. Alternately, the new
RACH resources may be a set of sub-frames that are different from the
sub-frames used by Rel8/9/10 UEs for RACH transmission. Alternately, the
new RACH resources may be a set of code sequences that are different from
the code sequences used by Rel8/9/10 UEs for RACH transmission.
Alternately, the new RACH resources may be a set of preambles that are
different from the preambles used by Rel8/9/10 UEs for RACH transmission.
Alternately, the new RACH resources may be a different combination of
RB/sub-frame/code-sequence/preamble than the
RB/sub-frame/code-sequence/preamble combination used by rel8/9/10 UEs. A
Rel11 UE that transmits RACH in the new RACH resources can monitor EPDCCH
CSS/UESS after receiving TC-RNTI.

Dynamically Determining Whether to Use PDCCH or EPDCCH

[0099] In an embodiment of the invention illustrated in FIG. 12, the UE is
configured with periodic intervals (T1) during which it is required to
monitor both PDCCH and EPDCCH on UESS. During these intervals, the eNB
may schedule the UE using either PDCCH or EPDCCH. However, the blind
decodes are split between PDCCH and EPDCCH (not all aggregation levels
can be used for EPDCCH).

[0100] For example, if the UE is scheduled using EPDCCH during T1, it only
monitors for EPDCCH until the next occurrence of T1. That is, after the
first EPDCCH based scheduling, UE switches to EPDCCH-only mode and
monitors EPDCCH at all aggregation levels. After receiving ACK (positive
acknowledgement) to first EPDCCH based transmission, network assumes UE
has switched to EPDCCH-only mode. Likewise, if UE is scheduled using
PDCCH during T1, it monitors PDCCH at all aggregation levels until the
next occurrence of T1.

[0101] Variations are possible. For example, (1) The duration T1 can be
fixed. The mode in T2 could be based on the last control channel received
in T1 (i.e. switching of modes happens precisely at the end of T1 rather
than when UE is first scheduled). (2) If UE is not scheduled during T1,
it can use a default mode during T2 (e.g., PDCCH-only).

[0102] It is to be noted that the start of T1 can be aligned with the
start of DRX on duration. This results in having a short window at the
start of each DRX on duration where the UE monitors for both PDCCH and
EPDCCH and subsequently monitors only one of the two, based on what was
used for scheduling in the short window. T2 can include periods where the
UE is in active time (i.e., monitoring PDCCH or EPDCCH) and the periods
where the UE is in DRX (i.e., a low power sleep mode where it is not
monitoring either PDCCH or EPDCCH)

[0103] It can be seen from the foregoing that a novel and useful method
and system for receiving a control channel has been described. It is to
be noted that embodiments within the scope of the present disclosure may
also include computer-readable media for carrying or having
computer-executable instructions or data structures stored thereon. Such
computer-readable media can be any available media that can be accessed
by a general purpose or special purpose computer. By way of example, and
not limitation, such computer-readable media can comprise RAM, ROM,
EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or
other magnetic storage devices, or any other medium which can be used to
carry or store desired program code means in the form of
computer-executable instructions or data structures. When information is
transferred or provided over a network or another communications
connection (either hardwired, wireless, or combination thereof) to a
computer, the computer properly views the connection as a
computer-readable medium. Thus, any such connection is properly termed a
computer-readable medium. Combinations of the above should also be
included within the scope of the computer-readable media.

[0104] Embodiments may also be practiced in distributed computing
environments where tasks are performed by local and remote processing
devices that are linked (either by hardwired links, wireless links, or by
a combination thereof) through a communications network.

[0105] Computer-executable instructions include, for example, instructions
and data which cause a general purpose computer, special purpose
computer, or special purpose processing device to perform a certain
function or group of functions. Computer-executable instructions also
include program modules that are executed by computers in stand-alone or
network environments. Generally, program modules include routines,
programs, objects, components, and data structures, etc. that perform
particular tasks or implement particular abstract data types.
Computer-executable instructions, associated data structures, and program
modules represent examples of the program code means for executing steps
of the methods disclosed herein. The particular sequence of such
executable instructions or associated data structures represents examples
of corresponding acts for implementing the functions described in such
steps.

[0106] While the present disclosure and the best modes thereof have been
described in a manner establishing possession by the inventors and
enabling those of ordinary skill to make and use the same, it will be
understood that there are equivalents to the exemplary embodiments
disclosed herein and that modifications and variations may be made
thereto without departing from the scope and spirit of the disclosure,
which are to be limited not by the exemplary embodiments but by the
appended claims.

List of Acronyms

[0107] BS Base Station

[0108] CCE Control Channel Element

[0109] CoMP
Coordinated Multi-Point

[0110] CP Cyclical Prefix

[0111] CQI Channel
Quality Indicator

[0112] CRC Cyclic Redundancy Check

[0113] C-RNTI Cell
RNTI

[0114] CQI Channel Quality Information

[0115] CRS Common Reference
Signal

[0116] CSI Channel State Information

[0117] CSI-RS Channel State
Information Reference Signal

[0118] CSS Common Search Space

[0119] DCI
Downlink Control Information

[0120] DL Downlink

[0121] DMRS Demodulation
Reference Signal

[0122] eNB Evolved Node B

[0123] EPBCH Enhanced Physical
Broadcast Channel

[0124] EPDCCH Enhanced Physical Downlink Control
Channel

[0125] EPRE Energy Per Resource Element

[0126] E-UTRA Evolved
UTRA

[0127] FFT Fast Fourier Transform

[0128] HARQ Hybrid Automatic
Repeat Request

[0129] LTE Long-Term Evolution

[0130] MAC Media Access
Control

[0131] MBSFN Multicast-Broadcast Single Frequency Network

[0132]
MCS Modulation and Coding Schemes

[0133] MIB Master Information Block

[0134] MIMO Multiple-Input Multiple-Output

[0135] MU-Multi-User MIMO

[0136] MIMO

[0137] OFDMA Orthogonal Frequency Division Multiple Access

[0138] P/S-SCH Primary/Secondary Synchronization Channel

[0139] PBCH
Primary Broadcast Control Channel

[0140] PCID Physical Cell Identifier

[0141] PDCCH Physical Downlink Control Channel

[0142] PDCP Packet Data
Convergence Protocol

[0143] PDSCH Physical Downlink Shared Channel

[0144]
PHICH Physical Hybrid ARQ Channel

[0145] PRB Physical Resource Block

[0146] P-RNTI Paging RNTI

[0147] PSS Primary Synchronization Signal

[0148] QAM Quadrature Amplitude Modulation

[0149] QPSK Quadrature Phase
Shift-Keying

[0150] RACH Random Access Channel

[0151] RB Resource Block

[0152] RE Resource Element

[0153] REG Resource Element Group

[0154] RF
Radio Frequency

[0155] RNC Radio Network Controller

[0156] RNTI Radio
Network Temporary Identifier

[0157] RRC Radio Resource Control

[0158] RRH
Remote Radio Head

[0159] RS Reference Signal

[0160] SFN System Frame
Number

[0161] SIB System Information Block

[0162] SI-RNTI System
Information RNTI

[0163] S-RNTI Serving RNC RNTI

[0164] SSS Secondary
Synchronization Signal

[0165] TC-RNTI Temporary Cell RNTI

[0166] tm
Transmission Mode

[0167] TP Transmission Point

[0168] UE User Equipment

[0169] UERS UE-specific Reference Symbol

[0170] UESS UE-Specific Search
Space

[0171] UL Uplink

[0172] UMTS Universal Mobile Telecommunications
System

[0173] U-RNTI UTRAN RNTI

[0174] UTRAN UMTS Terrestrial Radio
Access Network

Patent applications by Ajit Nimbalker, Buffalo Grove, IL US

Patent applications by Murali Narasimha, Lake Zurich, IL US

Patent applications by Ravi Kuchibhotla, Gurnee, IL US

Patent applications by Ravikiran Nory, Buffalo Grove, IL US

Patent applications by Robert T. Love, Barrington, IL US

Patent applications by Vijay Nangia, Algonquin, IL US

Patent applications by Motorola Mobility LLC

Patent applications in class Signaling for performing battery saving

Patent applications in all subclasses Signaling for performing battery saving